Punch die for powder compacting, powder compacting equipment equipped with punch die, and forming method with an equipment

ABSTRACT

In a punch die for powder compacting, a powder compacting equipment equipped with the punch die, and a forming method with the equipment, for suppressing the occurrence of stress concentration in the die without changing a shape of a powder compacting body, the punch die is used to form a cylindrical member by powder compacting, which has a substantially cylindrical shape and has a protrusion portion formed on the inner peripheral side thereof to protrude in the axial direction or a stepped portion or a concave portion formed on the inner peripheral side thereof in the radial direction. The punch die has a substantially cylindrical shape, and has a protrusion portion formed on at least a part of the inner peripheral surface or the outer peripheral surface thereof to protrude toward the center axis. The punch die is divided into two upper and lower parts at a surface forming the same surface as a lower surface of the protrusion portion, and the division surfaces are mechanically connected to each other or adhered to each other by adhesive.

FIELD OF THE INVENTION

The present invention relates to a punch die for powder compacting, a powder compacting equipment equipped with the punch die, and a forming method with the equipment which are used to manufacture a cylindrical member, having a protrusion portion formed on the inner peripheral side or the outer peripheral side of a cylindrical structure to protrude in the axial direction, by powder compacting.

DESCRIPTION OF RELATED ART

A powder compacting body having a protrusion portion formed on the inner peripheral side or the outer peripheral side thereof is used in a motor core or the like as a powder magnetic core. For example, in the motor core, a three dimensional powder magnetic core is used having protrusion portions discretely formed in the circumferential direction on an inner peripheral portion of a ring structure. An increase in the density of the powder compacting body contributes to the improvement in motor output power and motor torque. JP-A-2007-124884 discloses a rotating electrical machine in which a stator core is formed by compressing magnetic powder.

FIG. 2A is a perspective view of a cylindrical powder compacting body 200 formed by powder compacting disclosed in JP-A-2007-124884, and FIG. 2B is an enlarged perspective view showing a part A in FIG. 2A on an inner peripheral surface side. The cylindrical powder compacting body 200 includes a donut-shaped or cylindrical body portion 210, where a protrusion portion 220 is formed on the inner peripheral side of the body portion 210 to protrude in the axial direction, or a stepped portion or a concave portion is formed in the radial direction between the outer surface and the inner surface of the body portion 210.

Hereinafter, an example of the related art of a punch die for powder compacting, a powder compacting equipment with the punch die, and a forming method with the equipment for manufacturing the cylindrical powder compacting body 200 will be described.

FIGS. 4A and 4B show a shape of an upper punch die 400 of a punch die for powder compacting for manufacturing the powder compacting body 200 of FIG. 2A., where FIG. 4A is a perspective view of the upper punch die 400 when obliquely seen from the upper side thereof, and FIG. 4B is a perspective view of the upper punch die 400 when obliquely seen from the lower side thereof. The upper punch die 400 includes a ring portion 410 and a protrusion portion 420 which is formed on the inner peripheral side of the ring portion 410 to protrude in the radial direction. An upper surface 211 of the ring portion of the powder compacting body is pressed by a bottom surface 411 of the ring portion 410, and an upper surface 221 of the protrusion portion of the powder compacting body is pressed by a lower surface 421 of the protrusion portion 420. It is noted that in FIG. 2B, reference number 222 denotes an outer surface of the protrusion portion 220.

FIGS. 12A and 12B are cross-sectional views showing a structure of a main part of a powder compacting equipment 1200 with the upper punch die when taken along the line B-B′ of FIG. 4A, and a forming method thereof. The powder compacting equipment 1200 includes an inner peripheral core die 1210, an outer peripheral die 1220, an upper punch die 1230 for pressing powder 1201 from the upside thereof to apply a pressure thereto, and a lower punch die 1240 for pressing the powder from the downside thereof to apply a pressure thereto. A powder compacting body 1202 is formed by relatively moving the upper punch die 1230 and the lower punch die 1240.

In the above-described configuration, a problem arises in that cracking occurs due to stress concentration in a corner portion 430 of the upper punch die 400. During a powder compacting operation, a pressure applied by a press machine is added to the lower surface 421 of the protrusion portion of the upper punch die 400, and a lateral pressure is added to the inner peripheral surface 412 of the ring portion of the upper punch die 400 in accordance with the compacting of the powder. Accordingly, strong tensile stress occurs in the corner portion 430. For this reason, in the past, the stress concentration was alleviated by forming a curved surface in the corner portion 430. Meanwhile, as shown in FIGS. 2A and 2B, the same curved surface is formed at the corresponding position of the powder compacting body 200. Likewise, in the method of the related art, a degree of freedom in design of the powder compacting body is restricted in that the unnecessary curved surface is formed in the powder compacting body. For example, when the powder compacting body is used in the motor core shown in JP-A-2007-124884, the iron amount of the protrusion portion is reduced. For this reason, motor output power or motor torque is reduced, and hence sufficient characteristics cannot be obtained in some cases.

BRIEF SUMMARY OF THE INVENTION

Therefore, an object of the invention is to provide a punch die for powder compacting, a powder compacting equipment equipped with the punch die, and a forming method with the equipment, which are capable of suppressing stress concentration in a punch die without changing a shape of a powder compacting body.

In order to achieve the above-described object, according to an aspect of the invention, there is provided a punch die for powder compacting, which is used to form a cylindrical member by powder compacting, the cylindrical member having a substantially cylindrical shape and having a protrusion portion formed on the inner peripheral side or the outer peripheral side thereof to protrude in the axial direction or a stepped portion or a concave portion formed on the inner peripheral side or the outer peripheral side thereof in the radial direction, wherein the punch die has a substantially cylindrical shape and has a protrusion portion formed on at least a part of the inner peripheral surface or the outer peripheral surface thereof to protrude toward the center axis, and wherein the punch die is divided into two upper and lower parts at a surface forming the same surface as a lower surface of the protrusion portion, and the divided surfaces are mechanically connected to each other or adhered to each other by adhesive.

In addition, in the punch die for powder compacting of the invention, the upper and lower divided punch dies may be connected to each other at the division surfaces by bolt fastening, screw fastening, or fitting performed by forming a concave portion in one punch die and forming a convex portion in the other punch die.

Further, in the punch die for powder compacting of the invention, the lower punch die of the two upper and down divided punch dies may be exchangeable to correspond to the shape of the cylindrical member formed by powder compacting.

Furthermore, in the punch die for powder compacting of the invention, a corner portion as a connection portion connecting the lower surface of the protrusion portion to the inner peripheral surface of the down punch die may have at least one of an angular shape with a non-curved surface, a shape which satisfies R/δ<0.2 mm where a curvature radius of the corner portion is denoted by R and a radial width of the protrusion portion is denoted by δ and a shape which satisfies R<0.2 mm where a curvature radius of the corner portion is denoted by R.

Moreover, the punch die for powder compacting of the invention may further include: the above mentioned punch die for powder compacting as an upper punch; a lower punch die which is disposed to face the upper punch die in the axial direction; a die which is disposed on the outside of the upper punch die and the lower punch die; and a core die which is disposed on the inside of the upper punch die and the lower punch die, wherein powder filled between the upper punch die and the lower punch die is subjected to powder compacting by relatively moving the upper punch die and the lower punch die.

Further, in the invention, by using the above mentioned punch die for powder compacting, the lower punch die may be divided into an inner punch die and an outer punch die to have a diameter substantially corresponding to the outer diameter of the protrusion portion of the cylindrical member. The powder is subjected to powder compacting by relatively moving the upper punch die, the inner punch die, and the outer punch die.

Further, in order to achieve the above-described object, according to still another aspect of the invention, there is provided a method of forming a cylindrical member by powder compacting comprising of the steps: disposing a lower punch die to face an upper punch die in the axial direction, which upper punch die has a protrusion portion formed on at least a part of the inner peripheral surface thereof to protrude toward the center axis, is divided into two upper and lower parts at a surface forming the same surface as a lower surface of the protrusion portion, and is mechanically connected to each other or adhered to each other by adhesive; disposing a die on the outside of the upper punch die and the lower punch die; disposing a core die on the inside of the upper punch die and the lower punch die; and, subjecting powder filled between the upper punch die and the lower punch die to powder compacting by relatively moving the upper punch die and the lower punch die, to thereby form a cylindrical member having a substantially cylindrical shape and having a stepped portion or a concave portion formed on the inner peripheral side thereof.

Furthermore, in the method of forming the cylindrical member of the invention, the upper and lower divided punch dies may be connected to each other at the division surfaces by bolt fastening, screw fastening, or fitting performed by forming a concave portion in one punch die and forming a convex portion in the other punch die.

Moreover, in the method of forming the cylindrical member of the invention, the down punch die of the two upper and down divided punch dies may be exchangeable to correspond to the shape of the cylindrical member formed by powder compacting.

In addition, in the method of forming the cylindrical member of the invention, a corner portion as a connection portion connecting the lower surface of the protrusion portion to the inner peripheral surface of the down punch die may have at least one of an angular shape with a non-curved surface, a shape which satisfies at least any one of R/δ<0.2 where a curvature radius of the corner portion is denoted by R and a radial width of the protrusion portion is denoted by δ, and a shape which satisfies R<0.2 mm where a curvature radius of the corner portion is denoted by R.

Further, according to still another aspect of the invention, there is provided a powder compacting equipment for a cylindrical member, including: the punch die used in the above mentioned method of forming the cylindrical member by powder compacting as an upper punch die; a lower punch die which is disposed to face the upper punch die in the axial direction; a die which is disposed on the outside of the upper punch die and the lower punch die; and a core die which is disposed on the inside of the upper punch die and the lower punch die, wherein powder filled between the upper punch die and the lower punch die is subjected to powder compacting by relatively moving the upper punch die and the lower punch die.

Furthermore, in the powder compacting equipment of the invention, the lower punch die is divided into an inner punch die and an outer punch die to have a diameter substantially corresponding to the outer diameter of the protrusion portion of the cylindrical member. The powder is subjected to powder compacting by relatively moving the upper punch die, the inner punch die, and the outer punch die.

In the punch die of the invention, since the protrusion portion is divided into two parts, it is difficult to damage the corner portion due to the following reasons:

1) Since the inner peripheral surface of the cylindrical portion and the lower surface of the protrusion portion of the punch die are not integrated with each other in a view of material, stress of the lower surface and the inner peripheral surface is not applied to the corner portion.

2) Although a large load is applied to the protrusion portion of the punch die, tensile stress of the protrusion portion becomes weak due to the structure in which the punch die is divided at the surface forming the same surface as the lower surface of the protrusion portion of the punch die, and the divided punch dies are connected to each other.

3) Since the punch die is divided at the protrusion portion, cracking does not develop.

For these reasons, it is possible to reduce stress concentration in the corner portion which is the connection portion connecting the lower surface of the protrusion portion of the punch die to the inner peripheral surface of the cylindrical portion connected thereto.

Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1A is a perspective view showing a powder compacting body formed by a powder compacting equipment of a first embodiment according to the invention, and FIG. 1B is an enlarged perspective view showing an outer peripheral surface of a part F in FIG. 1A.

FIG. 2A is a perspective view showing a powder compacting body formed by a conventional powder compacting equipment, and FIG. 2B is an enlarged perspective view showing an outer peripheral surface of a part A of FIG. 2A.

FIGS. 3A and 3B show a structure of a punch die of the first embodiment, and FIG. 3A is a perspective view of a punch die of which upper and down punch dies are connected to each other, and FIG. 3B is a perspective view of the punch die of which the upper and down punch dies are separated from each other.

FIGS. 4A and 4B show a shape of a conventional punch die, and FIG. 4A is a perspective view when obliquely seen from the upside of the punch die, and FIG. 4B is a perspective view when obliquely seen from the downside of the punch die.

FIGS. 5A and 5B are cross-sectional views of a structure of a main part of a powder compacting equipment with an upper punch die of a second embodiment according to the invention when taken along the line C-C′ in FIG. 3A.

FIGS. 6A and 6B show a conventional example.

FIGS. 7A and 7B are cross-sectional views of a structure of a main part of a powder compacting equipment of a fourth embodiment according to the invention.

FIG. 8A is a perspective view showing a powder compacting body formed by the powder compacting equipment of the third embodiment, and FIG. 8B is an enlarged perspective view showing an outer peripheral surface of a part I in FIG. 8A.

FIGS. 9A and 9B show a structure of a punch die of the third embodiment, and FIG. 9A is a perspective view of the punch die of which the upper and down punch dies are connected to each other, and FIG. 9B is a perspective view of the punch die of which the upper and down punch dies are separated from each other.

FIG. 10 is a perspective view showing a powder compacting body formed by the powder compacting equipment of the fourth embodiment.

FIGS. 11A and 11B are cross-sectional views of a structure of a main part of the powder compacting equipment with the upper punch die of the first embodiment when taken along the line C-C′ of FIG. 3A.

FIGS. 12A and 12B are cross-sectional views of a structure of a main part of the powder compacting equipment with the upper punch die of the conventional punch die when taken along the line B-B′ of FIG. 4A.

FIGS. 13A and 13B are cross-sectional views of a structure of a main part of a powder compacting equipment of a fifth embodiment according to the invention.

FIGS. 14A to 14C are perspective views showing an example in which the powder compacting body formed by the powder compacting equipment of the fourth embodiment is applied to a stator of a motor.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments according to the invention will be described with reference to the accompanying drawings.

First Embodiment

FIGS. 3A and 3B show a structure of a punch die 300 of a first embodiment, where FIG. 3A is a perspective view of the punch die 300 of which an upper punch die 310 and a down punch die 320 are connected to each other, and FIG. 3B is a perspective view of the punch die 300 of which the upper punch die 310 and the down punch die 320 are separated from each other.

As shown in FIG. 3A, the punch die of the first embodiment is used to form a shape of a protrusion portion in a body portion of a powder compacting body, and is formed in a substantially cylindrical shape, and three protrusion portions 330 formed in the upper inner peripheral surface of the punch die to protrude toward the center axis are arranged in the circumferential direction.

As shown in FIG. 3B, a punch die 300 is divided into two parts at the surface forming the same surface as the lower surface of the protrusion portion 330. That is, the punch die 300 is divided into an upper punch die 310 and a down punch die 320, and the division surface of the punch die forms the same surface as the lower surface of the protrusion portion.

The upper and down punch dies are connected to each other at the division surface in accordance with a dividable connection method. For example, the upper and down punch dies can be strongly connected to each other in such a manner that a bolt (not shown) is attached to the down punch die, a nut (not shown) is attached to the upper punch die corresponding to the down punch die, and then the upper and down punch dies are connected to each other by bolt fastening.

The method of fastening the upper and down punch dies is not limited to the bolt fastening. For example, a concave portion is formed in one of the division surfaces of the upper and down punch dies, and a convex portion is formed in the other thereof, and the concave and convex portions are fitted to each other, so as to connect the upper and down punch dies by press fitting or the like.

In addition, the connection of the upper and down punch dies may be performed by adhesive or the like, or screw fastening.

As described above, the punch die has a structure in which the upper and down punch dies are connected to each other at the flat division surface formed by the lower surface of the upper punch die and the upper surface of the down punch die.

For this reason, a corner portion 340 (not shown) formed by the inner peripheral surface 321 and a lower surface 331 of the protrusion portion, to be provided with a step of the punch die, can be formed in a non-curved shape, for example, substantially at a right angle.

FIGS. 11A and 11B are cross-sectional views of a structure of a main part of a powder compacting equipment 1100 with the upper punch die when taken along the line C-C′ of FIG. 3A thereof as an upper punch die 1130. FIG. 11A shows the structure of the equipment when the upper punch die is moved up before the powder compacting operation. FIG. 11B shows the structure of the equipment immediately after the powder compacting operation of moving down the upper punch die 1130, and moving down the lower punch die 1140 to press powder 1101 and to form a powder compacting body 1102, and before the extraction operation of extracting the powder compacting body 1102.

FIGS. 11A and 11B, on the left side with respect to the central axis D, show the structure of the punch die portion with the protrusion portion in the equipment, and on the right side with respect to the central axis D, show the structure of the punch die portion without the protrusion portion in the equipment.

As shown in FIG. 11A, in the powder compacting equipment 1100, a lower punch die 1140 is disposed at the outside portion of the outer peripheral surface of the core die 1100 to apply a pressing force from the downside. In addition, a die 1120 is disposed at the outside portion of the outer peripheral surface of the lower punch die 1140. An upper punch die 1130 is disposed above a space E formed by the die 1120, the core die 1110, and the lower punch die 1140 to apply a pressing force from the upside.

In the powder compacting equipment 1100 with this configuration, as shown in FIG. 11A, the powder 1101 is filled into the space E formed by the die 1120, the core die 1110, and the lower punch die 1140. Then, as depicted by the white arrow of FIG. 11B, the upper punch die 1130 is moved down to apply a load to the powder 1101 from the upside thereof, and the lower punch die 1140 is moved down to apply a load to the powder 1101 from the downside thereof. As described above, the powder compacting body 1102 is formed by performing the powder compacting operation of pressing the powder 1101 by the use of the die 1120, the core die 1110, the lower punch die 1140, and the upper punch die 1130.

In addition, the powder compacting body having a structure shown in FIG. 1 is formed in such a manner that a powder magnetic core material is used as powder, and a load is applied from the powder compacting equipment of the press machine thereto to have the total density of the powder compacting body in which the powder magnetic material constituting the powder is not less than 92% of true density.

Further, FIG. 1A is a perspective view showing a powder compacting body 100 formed by the powder compacting equipment 1100, and FIG. 1B is an enlarged perspective view showing an outer peripheral surface of a part F of the powder compacting body 100 shown in FIG. 1A.

As shown in FIGS. 1A, 1B, 11A, and 11B, the powder compacting body 100 having three protrusion portions 120 formed on the upper surface of the donut-shaped body portion 110 in the circumferential direction is formed by using the powder compacting equipment 1100.

The powder compacting body 100 has a substantially cylindrical shape, and has the protrusion portion 120 formed on the inner peripheral side thereof to protrude in the axial direction or the stepped portion or the concave portion formed in the radial direction, that is, the stepped portion or the concave portion formed in the radial direction to form the protrusion portion 120.

However, in the punch die 400 shown in FIG. 4, cracking occurs due to stress concentration in the corner portion 430 during the powder compacting operation, and hence the punch die is damaged after a short period of time.

Since the load applied to the punch die becomes larger as the true density of the powder of the powder compacting body becomes higher, the life span of the punch die becomes shorter.

On the contrary, since the punch die 300 of the first embodiment has a structure in which the punch die 300 is vertically divided into two parts, that is, the upper punch die 310 and the down punch die 320 at the surface forming the same surface as the lower surface of the protrusion portion, as shown in FIG. 3, stress concentration does not occur in the corner portion (not shown) formed by the inner peripheral surface 321 and the lower surface 331 of the protrusion portion of the punch die 300 because of the forming of the corner portion by the separate upper punch die 310 and the separate down punch die 320, and excessive stress is prevented from being applied to the punch die 300, thereby preventing the damage thereto.

In addition, in this embodiment, the powder compacting body 100 shown in FIGS. 1A and 1B may have a structure in which a curvature radius 123 in a connection portion of a front end surface 121 and an outer peripheral surface 122 of the protrusion portion 120 is almost zero.

On the other hand, in the case of FIG. 2, since a corner portion 223 of the powder compacting body 200 shown in FIG. 2B has a curved shape, the area of the flat region of the front end surface 221 becomes small.

Likewise, when the flatness of the front end surface of the protrusion portion of the powder compacting body is improved, the following effects can be obtained.

1) In the case where the front end surface of the protrusion portion of the powder compacting body is overlapped, when the front end surface of the protrusion portion is flat, it is possible to further improve the adhesion force.

2) It is desirable that all end surfaces constituted by the front end surface of the powder compacting body are flat on the ground so that the powder compacting body for the equipment having a narrow width can be decreased in thickness.

3) In the application of forming a motor core or the like using a powder magnetic core material, since the iron amount is increased in the same physical shape by avoiding the unnecessary curved shape, the motor output power or motor torque is increased.

In addition, in the first embodiment described above, as shown in FIG. 1, the case is shown in which the number of the protrusion portions of the powder compacting body is three, but the same effect is exhibited even when the number of the protrusion portions is not three.

Second Embodiment

A second embodiment will be described with reference to FIGS. 5A and 5B. FIGS. 5A and 5B are cross-sectional views showing a structure of a main part of powder compacting equipment 500 of the second embodiment. FIG. 5A shows the structure of the equipment when an upper punch die 530 is moved up before the powder compacting operation, and FIG. 5B shows the structure of the equipment immediately after the powder compacting operation of moving down the upper punch die 530, and moving down a lower outer punch die 540 and a lower inner punch die 550 to press powder 501 and to form a powder compacting body 502, and before the extraction operation of extracting the powder compacting body 502. It is noted that in FIG. 5A, reference numeral 510 denotes a core die, and 520 denotes a die.

As shown in FIG. 5A, in this embodiment, the lower punch die pressing the lower surface of the powder compacting body is divided into two parts, that is, the lower inner punch die 550 and the lower outer punch die 540. When the lower outer punch die 540 is moved up before the powder compacting operation, it is possible to allow the height of the powder of the body portion 110 of the powder compacting body shown in FIG. 1 to be lower than the height of the powder of the protrusion portion 120 of the powder compacting body.

In the state of FIG. 5A, the upper punch die 530 is moved down to press the powder 501. Simultaneously, the lower outer punch die 540 is moved down, while applying a load upward, up to a position at which an upper surface 541 of the lower outer punch die 540 is substantially aligned to an upper surface 551 of the lower inner punch die 550.

With the above-described configuration, it is possible to allow the compression amount of the powder in the body portion 110 of the powder compacting body to be substantially equal to the compression amount of the powder in the protrusion portion 120. That is, it is possible to perform the powder compacting operation while uniformizing the densities of the protrusion portion 120 and the body portion 110 of the powder compacting body.

Likewise, when the densities of the protrusion portion and the body portion of the powder compacting body are uniformized, the following effects can be obtained.

1) It is possible to uniformize the strength of the powder compacting body in the body portion and the protrusion portion.

2) In the application of forming a motor core or the like using a powder magnetic core, magnetic characteristics such as saturation flux density or iron loss are substantially uniformized in the motor core.

Third Embodiment

A third embodiment will be described with reference to FIGS. 8A, 8B, 9A, and 9B. FIG. 9A shows a structure of a punch die 900 of the third embodiment, and is a perspective view of the punch die 900 of which an upper punch die 910 and a down punch die 920 are connected to each other. FIG. 9B is a perspective view of the punch die 900 of which the upper punch die 910 and the down punch die 920 are separated from each other.

As shown in FIG. 9A, the punch die 900 of the third embodiment is used to form the shape of the protrusion portion in the body portion of the powder compacting body, and is formed in a substantially cylindrical shape, and three protrusion portions 930 formed on the upper inner peripheral surface of the punch die to protrude toward the center axis are arranged in the circumferential direction. A lower surface 931 of the protrusion portion 930 is formed in a double-stage tapered shape in the axial direction to be inclined downward from the inner peripheral side to the outer peripheral side.

As shown in FIG. 9B, the punch die 900 is vertically divided into two parts at a position where the inclinations of the tapered lower surfaces 931 of the protrusion portions 930 are different. That is, the punch die 900 includes an upper punch die 910 and a down punch die 920 which are separable from each other, and the division surface of the punch die 900 forms the same surface as the lower surface of the protrusion portion.

The upper and down punch dies are connected to each other at the division surface in accordance with a dividable connection method. For example, the upper and down punch dies can be strongly connected to each other in such a manner that a bolt (not shown) is attached to the down punch die, a nut (not shown) is attached to the upper punch die corresponding to the down punch die, and then the upper and down punch dies are connected to each other by bolt fastening.

The method of fastening the upper and down punch dies to each other is not limited to the bolt fastening. For example, the upper and down punch dies 910 and 920 may be connected to each other in such a manner that a concave portion is formed in one of the division surfaces of the upper and down punch dies, and a convex portion is formed in the other thereof, and the concave and convex portions are fitted to each other so as to connect them by press fitting.

In addition, the connection of the upper and down punch dies may be performed by adhesive or the like, or screw fastening.

As described above, the punch die 900 has a structure in which the upper and down punch dies 910 and 920 are connected to each other at the division surface having a flat face formed by the lower surface of the upper punch die and the upper surface of the down punch die.

In addition, FIG. 8A is a perspective view showing a powder compacting body 800 formed by the powder compacting equipment 500 using the punch die 900 of FIG. 9A as the upper punch die, and FIG. 8B is an enlarged perspective view showing an outer peripheral surface of a part I of the powder compacting body 800 shown in FIG. 8A.

The powder compacting body 800 having three protrusion portions 820 formed on an upper surface of a donut-shaped body portion 810 in the circumferential direction is formed on the upper surface of the body portion 810 having a donut-shaped structure by using the powder compacting equipment 500 shown in FIG. 8A.

The powder compacting body 800 has a substantially cylindrical shape, and has the protrusion portion 820 formed on the inner peripheral side thereof to protrude in the axial direction or the stepped portion or the concave portion formed in the radial direction, that is, the stepped portion or the concave portion formed in the radial direction to form the protrusion portion 820. The upper surface 821 of the protrusion portion 820 of the powder compacting body 800 is provided with a taper 823 which is formed in the circumferential direction to be inclined downward from the inner peripheral side to the outer peripheral side. The upper surface 821 of the protrusion portion 820 is provided with a taper 824 which is formed in the radial direction to be inclined downward from the inside to the outside. An outer peripheral surface 822 of the protrusion portion 820 is provided with a taper 825 which is formed from the upper end to the lower end to be enlarged toward the outer peripheral side.

Likewise, when the taper is formed in the punch die, the following effect can be obtained.

1) Since the protrusion portion of the powder compacting body is thinned in the axial direction, it is easy to extract the upper punch die from the powder compacting body after the powder compacting operation.

Fourth Embodiment

A case of performing a powder compacting operation on a stator core of a three dimension (3D) motor of a fourth embodiment will be described with reference to FIGS. 7A, 7B, 10, and 14A to 14C.

FIG. 7A is a cross-sectional view showing a structure of a main part of a powder compacting equipment 700 for performing the powder compacting operation on the 3D motor core, and shows the structure of the equipment of which an upper punch die 730 is moved up before the powder compacting operation. FIG. 7B shows the structure of the equipment immediately after the powder compacting operation of moving down the upper punch die 730 and moving down the lower punch die to press the powder and to form a powder compacting body 702, and before the extraction operation of extracting the powder compacting body 702.

FIGS. 7A and 7B, on the left side of the central axis D, show the structure of the punch die portion with the protrusion portion in the equipment, and on the right side of the central axis D, show the structure of the punch die portion without the protrusion portion in the equipment.

As shown in FIG. 7A, in the powder compacting equipment 700, a lower inner punch die 750 and a lower outer punch die 740 are disposed at the outside portion of the outer peripheral surface of a core die 710 to apply a pressing force from the downside. In addition, a die 720 is disposed at the outside portion of the outer peripheral surface of the lower outer punch die 740. An upper punch die 730 is disposed above a space K formed by the die 720, the core die 710, the lower inner punch die 750, and the lower outer punch die 740 to apply a pressing force from the upside.

In the powder compacting equipment 700 with this configuration, as shown in FIG. 7A, powder 701 is filled into the space K formed by the die 720, the core die 710, the lower inner punch die 750, and the lower outer punch die 740. Then, as depicted by the white arrow of FIG. 7B, the upper punch die 730 is moved down to apply a load to the powder 701 from the upside thereof, and the lower outer punch die 740 is moved down to apply a load to the powder 701 from the downside thereof. As described above, the powder compacting body 702 is formed by performing the powder compacting operation of pressing the powder 701 by the use of the die 720, the core die 710, the lower inner punch die 750, the lower outer punch die 740, and the upper punch die 730.

In addition, the powder compacting body having a structure shown in FIGS. 10 and 14A to 14C is formed in such a manner that a powder magnetic core material is used as powder, and a load is applied from the powder compacting equipment of the press machine thereto so that the total density of the powder compacting body in which the powder magnetic material constitutes the powder is not less than 92% of true density.

Further, FIG. 10 is a perspective view showing a powder compacting body 1000 formed by the powder compact equipment 700, and FIGS. 14A to 14C are perspective views showing an example in which a powder compacting body 1410 formed by the powder compacting equipment 700 is applied to a stator of a motor.

FIGS. 14A and 14C are respective perspective views of the stator of the motor of the powder compacting body 1410 formed by the powder compacting equipment 700, and FIG. 14B is a perspective view of a coil 1420 which is sandwiched by the stators of the motor of the powder compacting body 1410, for passing an electric current.

In the above-described configuration, a powder magnetic core material of iron is used, and a load is applied to the powder by using the upper and lower punch dies so that the total densities of the powder compacting body and the protrusion portion of the powder compacting body are not less than 92%.

In the past, in such a high density state, as shown in FIGS. 4A, 4B described above, stress concentration occurs in the corner portion 430 of the upper punch die 400, and hence the punch die 400 may be damaged after a short period of time. Since the load applied to the upper punch die becomes larger as the density of the material of the powder compacting body becomes higher, the life span of the upper punch die becomes shorter.

However, in the fourth embodiment, since a corner portion 731 of a punch die 730 is formed in the manner that the upper and down punch dies 732 and 733 are separated from each other and then connected to each other, it is possible to suppress the punch die 730 from being damaged.

By means of the above-described powder compacting operation, as shown in FIGS. 10, 14A, and 14C, a powder compacting body (1000 and 1410) having twelve protrusion portions 1020 formed on the upper surface of a ring-structured body 1010 in the circumferential direction is formed.

The powder compacting body has a substantially cylindrical shape, and has the protrusion portion 1020 formed on the inner peripheral side thereof to protrude in the axial direction, or the stepped portion or the concave portion formed in the radial direction, that is, the stepped portion or the concave portion formed in the radial direction to form the protrusion portion 1020.

In the powder compacting body 1000, as shown in FIGS. 7A and 7B, the punch die 730 of the powder compacting equipment 700 for forming the powder compacting body 1000 is divided into two parts, that is, the upper punch die 732 and the down punch die 733. In addition, a connection portion 1023 of a front end surface 1022 and the outer peripheral surface 1021 of the protrusion portion 1020 of the powder compacting body shown in FIG. 10 is formed by the inner peripheral surface of the down punch die and the lower surface of the protrusion portion of the upper punch die, as shown in FIG. 10. The connection portion 1023 of the powder compacting body can be formed in an angular shape such as a perpendicular surface having a non-curved structure and a non-perpendicular surface, and the front end surface 1022 can be formed as a flat surface.

In this embodiment, the punch die is divided only at the position 731 corresponding to the inner peripheral protrusion portion of the powder compacting body, but the punch die may be divided at the stepped portion 734 of the outer peripheral side of the powder compacting body. Further, both of them may be used together.

Likewise, when the flatness of the front end surface of the protrusion portion of the powder compacting body is improved, the following effects can be obtained.

1) When the front end surface of the protrusion portion of the powder compacting body is overlapped, it is possible to further improve the adhesion force on the flat surface. Since it is possible to maximize the connection surface in the front end surface having a large flat region during the connection between the front end surface and the planar material, it is possible to further improve the adhesion force, and to remove the unnecessary space.

2) It is desirable that the front end surface is flat on the ground that the powder compacting body for the equipment having a narrow width can be decreased in thickness.

In the fourth embodiment, the case has been described in which the curvature radius R is zero, but even when the curvature radius is not zero, if R/δ<0.2, or R<0.1 mm, the above-described effect can be sufficiently obtained. In addition, as shown in FIG. 10, δ indicates the width of the front end surface of the protrusion portion of the powder compacting body.

Then, as the value becomes smaller to be R/δ<0.1 and R/δ<0.05, the above-described effect is improved. As the curvature radius becomes a small value to be R<0.1 mm and R<0:05 mm, the above-described effect is improved.

When the total density of the powder compacting body becomes high to be not less than 92% of the true density of the material constituting the powder, the following effects can be obtained.

1) Since the powder compacting body becomes rigid in accordance with an increase in the density thereof, it is possible to improve the strength of the powder compacting body.

2) In the case of mounting the powder compacting body to a restricted space, the present invention is effective.

3) The powder compacting body can be formed by net shape manufacture and the productivity is improved.

In addition, when the powder compacting body is utilized in a motor core or the like using a powder magnetic core material, the following effect can be obtained.

4) Since the powder compacting body can be formed in a more desired shape, the distortion of magnetic flux is suppressed, and the density of magnetic flux is improved. Also, the motor output power or motor torque depending on the magnetic flux becomes large.

Then, since the maximum stress is reduced, the following effects are obtained.

1) Since the stress applied to the powder compacting body is averaged, it is possible to uniformize the density of the powder compacting body.

2) Since it is possible to reduce residual stress concentrating on a part of the powder compacting body, it is possible to reduce hysteresis loss.

3) In the case of using the insulatively coated powder magnetic core material as the powder, since the stress applied to the powder compacting body is averaged without concentration, the breakage of the insulating coating is prevented, and hence the eddy current loss is reduced.

4) Since the stress concentration in the punch die is prevented, it is possible to prolong the life span of the die without a risk of excessive stress.

5) As described above, the present invention is effective in the application to the components of the motor, the components of the actuator, or the loading components.

Fifth Embodiment

A fifth embodiment will be described with reference to FIGS. 13A and 13B. FIGS. 13A and 13B are cross-sectional views showing a structure of a main part of the fifth embodiment, and FIG. 13A shows a structure of an equipment 1300 of which an upper punch die 1330 is moved up before the powder compacting operation. FIG. 13B shows the structure of the equipment immediately after the powder compacting operation of moving down the upper punch die 1330, and moving down a lower inner punch die 1350 to press a powder 1301 and to form a powder compacting body 1302, and before the extraction operation of extracting the powder compacting body 1302.

The powder compacting body formed in this embodiment has a protrusion portion 1303 formed in the outer peripheral side thereof, but as in the fourth embodiment, the same effect is obtained by dividing the punch die into an upper punch die 1332 and a down punch die 1333 at a protrusion upper end portion or a counter portion 1331. In addition, the punch die may be divided at a stepped portion 1334 of the inner peripheral portion of the powder compacting body. Further, the same effect can be obtained even when both of them are used in combination.

It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. 

1. A punch die for powder compacting, which is used to form a cylindrical member by powder compacting, the cylindrical member having a substantially cylindrical shape and having a protrusion portion formed on the inner peripheral side or the outer peripheral side thereof to protrude in the axial direction or a stepped portion or a concave portion formed on the inner peripheral side or the outer peripheral side thereof in the radial direction, wherein the punch die has a substantially cylindrical shape, and has a protrusion portion formed on at least a part of the inner peripheral surface or the outer peripheral surface thereof to protrude toward the center axis, and wherein the punch die is divided into two upper and lower parts at a surface forming the same surface as a lower surface of the protrusion portion, and the division surfaces are mechanically connected to each other or adhered to each other by adhesive.
 2. The punch die for powder compacting a cylindrical member according to claim 1, wherein the upper and lower divided punch dies are connected to each other at the division surfaces by bolt fastening, screw fastening, or fitting performed by forming a concave portion in one punch die and forming a convex portion in the other punch die.
 3. The punch die for powder compacting a cylindrical member according to claim 1, wherein the down punch die of the two upper and lower divided punch dies is exchangeable to correspond to the shape of the cylindrical member to be formed by powder compacting.
 4. A punch die for powder compacting a cylindrical member according to claim 1, wherein a corner portion as a connection portion connecting the lower surface of the protrusion portion to the inner peripheral surface of the down punch die has an angular shape with a non-curved surface, or a shape which satisfies at least any one of R/δ<0.2 mm or R<0.2 mm, where a curvature radius of the corner portion is denoted by R, and a radial width of the protrusion portion is denoted by δ.
 5. A powder compacting equipment for a cylindrical member, comprising: an upper punch die which is the punch die for powder compacting for the cylindrical member of claim 1; a lower punch die which is disposed to face the upper punch die in the axial direction; a die which is disposed on the outside of the upper punch die and the lower punch die; and a core die which is disposed on the inside of the upper punch die and the lower punch die, wherein powder filled between the upper punch die and the lower punch die is subjected to powder compacting by relatively moving the upper punch die and the lower punch die.
 6. The powder compacting equipment according to claim 5, wherein the lower punch die is divided into an inner punch die and an outer punch die to have a diameter substantially corresponding to the outer diameter of the protrusion portion of the cylindrical member, and wherein the powder is subjected to powder compacting by relatively moving the upper punch die, the inner punch die, and the outer punch die.
 7. A method of forming a cylindrical member, comprising the steps of: disposing a lower punch die to face an upper punch die in the axial direction, the upper punch die having a protrusion portion formed in at least a part of the inner peripheral surface thereof to protrude toward the center axis, and being divided into two upper and lower parts at a surface forming the same surface as a lower surface of the protrusion portion, the divided surfaces being mechanically connected to each other or adhered to each other by adhesive; disposing a die on the outside of the upper punch die and the lower punch die; disposing a core die on the inside of the upper punch die and the lower punch die; and subjecting powder filled between the upper punch die and the lower punch die to powder compacting by relatively moving the upper punch die and the lower punch die to thereby form a cylindrical member having a substantially cylindrical shape and having a stepped portion or a concave portion formed on the inner peripheral side thereof.
 8. The method according to claim 7, wherein the upper and lower divided punch dies are connected to each other at the division surfaces by bolt fastening, screw fastening, or fitting performed by forming a concave portion in one punch die and forming a convex portion in the other punch die.
 9. The method according to claim 7, wherein the down punch die of the two upper and down divided punch dies is exchangeable to correspond to the shape of the cylindrical member to be formed by powder compacting.
 10. The method according to claim 7, wherein a corner portion as a connection portion connecting the lower surface of the protrusion portion to the inner peripheral surface of the down punch die has an angular shape with a non-curved surface or a shape which satisfies at least any one of R/δ<0.2 mm or R<0.2 mm, where a curvature radius of the corner portion is denoted by R, and a radial width of the protrusion portion is denoted by δ.
 11. A powder compacting equipment for a cylindrical member, comprising: an upper punch die which is the punch die for powder compacting for the cylindrical member of claim 7; a lower punch die which is disposed to face the upper punch die in the axial direction; a die which is disposed on the outside of the upper punch die and the lower punch die; and a core die which is disposed on the inside of the upper punch die and the lower punch die, wherein powder filled between the upper punch die and the lower punch die is subjected to powder compacting by relatively moving the upper punch die and the lower punch die.
 12. The powder compacting equipment according to claim 11, wherein the lower punch die is divided into an inner punch die and an outer punch die to have a diameter substantially corresponding to the outer diameter of the protrusion portion of the cylindrical member, and wherein the powder is subjected to powder compacting by relatively moving the upper punch die, the inner punch die, and the outer punch die. 